Variable-pitch airscrew



March 27, FNRHURST 2,372,416

VARIABLE-PITCH AIRSCREW Filed Feb. 11,1942 2 Sheets-Sheet 1 March 27, 1945. L. G. FAIRHURST 2,372,416

VARIABLE-PITCH AIRSCREW Filed Feb. 11, 1942 2 Sheets-Sheet. '2-

Patented Mar. 27, 1945 vAnIABLE-PrroH-AmscaEW V Leonard Gas kell Fairhurst, Gloucester, :England, I 7' assignor to Rotol Limited, 3.

ri a n r a yv of r a I Application February 11, 1942, Serial No. 430,459

a In Great Britain December 19, I940 2 Claims. (01. 170-5162) This invention relates to variable-pitch airscrews of the type in which each blade is mounted,- usually by an adaptor surroundingthe bla'de-rootgto rotate in bearings in the hub. The blade-root is subjected to high "centrifugal loads in the direction of its length and also to bending loads due to aero-dynamic forces, and it has hitherto been customary to form the bladerootwith a radial flange and a cylindrical-portion to carry these two loads respectivelyu The use of a flange has, however, two disadvantages in that its provision usually means that the stress-concentration at the root of the blade will be fairly high so that the root-diameter will'be greater thanwould otherwise be necessary; and that the formation of the flange also involves the interruption of the. grain flow in the material of the blade and a consequential weakness near the flange where the stress-concentration is greatest. These disadvantages are particularly serious when the airscrew blades are made of a light alloy, such'as an alloy of magnesium, which According to the present invention a blade for a variable-pitch airscrew has its root formed with a conical surface to engage a bearing, directly or indirectly, substantially normally to the direction of the resultant loading on the surface. This loading is due partly to centrifugal force acting along the axis of the blade and partly to the bending load acting normally of said axis so that the resultant load acts in a direction inclined to the axis of the blade.

The root of the blade is, preferably, formed to provide the conical surface by an upsetting or equivalent operation so that the-grain flow of the material is not unduly disturbed and weakness due to the interruption of the grain flow is avoided. The use of a conical surface eliminates sharp angle so that high stress-concentration is avoided in this portion of the blade.

It is a feature of this invention to form the root of the blade with a cylindrical surface spaced away from the conical surface to carry, or assist in carrying, the bending load on the blade.

The present invention also includes the combination with a blade arranged as set out above of an. adaptor comprising a longitudinally-divided two-part sleeve arranged to fit the cylindrical surface of the blade and formed with a conical surface to engage the conical surface on the blade, and means for securing the two parts of the blade together. The securing means may comprise an integral ring secured to the end of the sleeve nearest the base of the blade and means atthe other end of the sleeve for clamping its two fpartstogether, preferably against the cylindrical portion of the blade.

- The present invention also comprises .an

adaptor for the blade of a variable-pitch airscrew, comprising a longitudinally divided twopart sleeve whereof the abutting edges are serrated transversely -of "their length to interlock and prevent relative longitudinal movement of the two parts. I

.A blade and an adaptor for a variable-pitch airscrew will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a section through the blade and adaptor in the plane containing the axis-of the blade and the axis of the airscrew of which the blade forms part; this figure is a section on the line l-l of Figure 2;

Figure 215 an under plan of the blade and. adaptor;

Figure 3 is an elevation of the blade and adaptor as seen when looking in the direction of the arrow X in Figure 1, and

Figure 4 is a plan of a clamping ring employed.

The root IU of the blade is formed with a cylindrical surface H and with a conical surface I2 which is formed by an upsetting or equivalent operation. The surface I2 is substantially normal to the direction of the resultant load on this surface due to centrifugal and bending loads. The root I0 is supported in the adaptor which comprises a two-part sleeve I3 divided longitudinally at 14 (see Figure 3). The sleeve l3 fits the cylindrical surface H of the blade root and is formedwith a conical surface l5 to engage the conical surface l2 on the blade root. A ring 16 is bolted to the lower end of the sleeve l3, after the two parts have been placed around the blade-root, and has a lip I! which fits over the outer surface of the sleeve and holds the two parts of the sleeve together at this end. A clamping ring l8 (see Figure 4) is formed in two parts articulated together at l9 and tightenedround the upper end of the sleeve I3 by means of a nut and bolt 20. This clamping ring holds the upper ends ofthe two parts of the sleeve together and also clamps them against the cylindrical surface H of the blade-root. The abutting edges of'the two parts of the sleeve 13 are serrated at 2| (see Figure 3) and the serrations interlock to prevent relative longitudinal movement of the two parts. The serrations terminat-e short of the top of the sleeve in order to leave gaps between the two parts of the sleeve which enables the two parts to be clamped against the blade-root. The conical surfaces [2 and I5 are held in engagement with one another by a ring 22 which is screwed into the ring l6 and into engagement with the base of the blade-root so as to hold the surfaces l2 and IS in engagement Fri arranged to rotate the blade through bevel gearing including a bevel-wheel secured to the root of the blade, or which may be an hydraulic motor connected by a link to a pin on the blade. The present blade is arranged for pitch-variation by an hydraulic motor having a movable cylinder which is connected to a pin 25 on the base of the blade. It will be observed that this pin is integral with the ring l5 which is secured to the adaptor [3 so that the pitch-varying motor is operatively connected to the adaptor and rotates the adaptor which, in turn, rotates the blade root to which it is clamped. This has the advantage that the pitch of the blade can be adjusted by slackening the clamping ring l8, which is readily accessible, and turning the blade in the adaptor to the required pitch-setting, it being unnecessary to disturb the connection to the pitch-varying motor.

I claim:

1. For a variable-pitch airscrew, the combination with a blade whereof the root is formed with a cylindrical portion and a conical surface facing towards the tip of the blade, of a longitudi- K conical surfaces on the blade and the sleeve into 2. For a variable-pitch airscrew, the combination with a blade whereof the root is formed with a'cylindrical surface and a conical surface facing towards the tip of the blade and located between the cylindrical surface and the root end of the blade, of a sleeve longitudinally divided into two parts of which the abutting edges are serrated transversely of their length to interlock, fitting around the cylindrical portion of the bladeroot and formed with a conical surface engaged with that on the blade-root, a clamping ring tightened around the sleeve to clamp its two parts together against the cylindrical portion of the blade-root, an integral ring secured to the end of the sleeve nearest the root end of the blade and formed with a lip snugly surrounding the sleeve to hold its parts together, a member screwed into the integral ring to engage the end of the bladeroot and force the said conical surfaces together and a pin projecting from the integral ring.

LEONARD GASKELL FAIRHURSI. 

